字符设备驱动-8.休眠唤醒机制

1 休眠与唤醒

1.APP 调用 read 等函数试图读取数据，比如读取按键；
2.APP 进入内核态，也就是调用驱动中的对应函数，发现有数据则复制到用户空间并马上返回；
3.如果 APP 在内核态，也就是在驱动程序中发现没有数据，则 APP 休眠；
4.当有数据时，比如当按下按键时，驱动程序的中断服务程序被调用，它会记录数据、唤醒 APP；
5.APP 继续运行它的内核态代码，也就是驱动程序中的函数，复制数据到用户空间并马上返回

drv_read函数当没有数据时需要休眠等待有数据唤醒。当按下按键，驱动程序中的中断服务程序被调用，它会记录数据，并唤醒 APP的read函数。

1.0 引入上下文概念

app执行整个过程如下图，可以把它看作被拆分成2段：被叫做“上下文”。

1.0.1 进程上下文

或者这样说：红实线所涉及的代码，都是APP调用的，被叫做进程上下文，drv_read中有数据直接返回数据，没有数据的话让出CPU休眠等待。

1.0.1 中断上下文

但是按键的中断服务程序，不属于APP的 “上下文”，这是突如其来的，当中断发生时，APP1 正在休眠呢。在 APP 的“上下文”，也就是在 APP的执行过程中，它是可以休眠的。
在中断的处理过程中，也就是gpio_key_irq的执行过程中，它不能休眠：“中断”怎么能休眠？“中断”休眠了，谁来调度其他 APP 啊？
所以：在中断处理函数中，不能休眠，也就不能调用会导致休眠的函数, 被叫做中断上下文。

1.1 休眠函数

内核源码：include\linux\wait.h

参数1：wq: waitqueue等待队列
用来等待条件值，condition不为0则立即返回
参数2：condition
这可以是一个变量，也可以是任何表达式。表示“一直等待，直到 condition为真

1.2 唤醒函数

1.3 使用

1.read函数中进行wait_event_interruptible，因此需要初始化一个wq, 用init_waitqueue_head函数进行初始化等待队列。

wait_queue_head_t job_done_wq;
init_waitqueue_head(&job->job_done_wq);

或者用DECLARE_WAIT_QUEUE_HEAD声明定义初始化一起。

static DECLARE_WAIT_QUEUE_HEAD(gpio_key_wait);

read函数判断是否有key，有key则直接返回，否则wait_event_interruptible休眠。

wait_event_interruptible(gpio_key_wait, g_key);

2.如果按键按下了，中断isr进行响应，调用wake_up_interruptible,并且设置condition为true.驱动的read函数将会被唤醒。

驱动代码

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/platform_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/slab.h>

struct gpio_key{
	int gpio;
	struct gpio_desc *gpiod;
	int flag;
	int irq;
} ;

static struct gpio_key *gpio_keys_100ask;
static int major = 0;
static struct class *gpio_key_class;
static int g_key = 0;
static DECLARE_WAIT_QUEUE_HEAD(gpio_key_wait);

static ssize_t gpio_key_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset){
	int err;

	wait_event_interruptible(gpio_key_wait, g_key);
	err = copy_to_user(buf, &g_key, 4);
	g_key = 0;
	return 4;
}

static struct file_operations gpio_key_drv = {
	.owner	 = THIS_MODULE,
	.read    = gpio_key_drv_read,
};

static irqreturn_t gpio_key_isr(int irq, void *dev_id){
	struct gpio_key *gpio_key = dev_id;
	int val;

	val = gpiod_get_value(gpio_key->gpiod);
	printk("key %d %d\n", gpio_key->gpio, val);
	g_key = (gpio_key->gpio << 8) | val;
	wake_up_interruptible(&gpio_key_wait);
	return IRQ_HANDLED;
}

/* 1. 从platform_device获得GPIO
 * 2. gpio=>irq
 * 3. request_irq
 */
static int gpio_key_probe(struct platform_device *pdev){
	int err;
	struct device_node *node = pdev->dev.of_node;
	int count;
	int i;
	enum of_gpio_flags flag;

	count = of_gpio_count(node);
	if (!count){
		printk("%s %s line %d, there isn't any gpio available\n", __FILE__, __FUNCTION__, __LINE__);
		return -1;
	}

	gpio_keys_100ask = kzalloc(sizeof(struct gpio_key) * count, GFP_KERNEL);
	for (i = 0; i < count; i++){
		gpio_keys_100ask[i].gpio = of_get_gpio_flags(node, i, &flag);
		if (gpio_keys_100ask[i].gpio < 0){
			printk("%s %s line %d, of_get_gpio_flags fail\n", __FILE__, __FUNCTION__, __LINE__);
			return -1;
		}
		gpio_keys_100ask[i].gpiod = gpio_to_desc(gpio_keys_100ask[i].gpio);
		gpio_keys_100ask[i].flag = flag & OF_GPIO_ACTIVE_LOW;
		gpio_keys_100ask[i].irq  = gpio_to_irq(gpio_keys_100ask[i].gpio);
	}

	for (i = 0; i < count; i++){
		err = request_irq(gpio_keys_100ask[i].irq, gpio_key_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "100ask_gpio_key", 			&gpio_keys_100ask[i]);
	}

	major = register_chrdev(0, "100ask_gpio_key", &gpio_key_drv);  /* /dev/100ask_gpio_key */
	gpio_key_class = class_create(THIS_MODULE, "100ask_gpio_key_class");
	if (IS_ERR(gpio_key_class)) {
		printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
		unregister_chrdev(major, "100ask_gpio_key");
		return PTR_ERR(gpio_key_class);
	}
	device_create(gpio_key_class, NULL, MKDEV(major, 0), NULL, "100ask_gpio_key"); /* /dev/100ask_gpio_key */
    return 0;
}
static int gpio_key_remove(struct platform_device *pdev){
	struct device_node *node = pdev->dev.of_node;
	int count;
	int i;
	device_destroy(gpio_key_class, MKDEV(major, 0));
	class_destroy(gpio_key_class);
	unregister_chrdev(major, "100ask_gpio_key");
	count = of_gpio_count(node);
	for (i = 0; i < count; i++){
		free_irq(gpio_keys_100ask[i].irq, &gpio_keys_100ask[i]);
	}
	kfree(gpio_keys_100ask);
    return 0;
}

static const struct of_device_id ask100_keys[] = {
    { .compatible = "100ask,gpio_key" },
    { },
};
static struct platform_driver gpio_keys_driver = {
    .probe      = gpio_key_probe,
    .remove     = gpio_key_remove,
    .driver     = {
        .name   = "100ask_gpio_key",
        .of_match_table = ask100_keys,
    },
};
static int __init gpio_key_init(void){
    int err;
    err = platform_driver_register(&gpio_keys_driver); 
	return err;
}
static void __exit gpio_key_exit(void){
    platform_driver_unregister(&gpio_keys_driver);
}
module_init(gpio_key_init);
module_exit(gpio_key_exit);
MODULE_LICENSE("GPL");

驱动代码2(使用环形buf存放键值)

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/platform_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/slab.h>

struct gpio_key{
	int gpio;
	struct gpio_desc *gpiod;
	int flag;
	int irq;
} ;
static struct gpio_key *gpio_keys_100ask;
static int major = 0;
static struct class *gpio_key_class;

/* 环形缓冲区 */
#define BUF_LEN 128
static int g_keys[BUF_LEN];
static int r, w;
#define NEXT_POS(x) ((x+1) % BUF_LEN)
static int is_key_buf_empty(void){
	return (r == w);
}
static int is_key_buf_full(void){
	return (r == NEXT_POS(w));
}
static void put_key(int key){
	if (!is_key_buf_full()){
		g_keys[w] = key;
		w = NEXT_POS(w);
	}
}
static int get_key(void){
	int key = 0;
	if (!is_key_buf_empty()){
		key = g_keys[r];
		r = NEXT_POS(r);
	}
	return key;
}

static DECLARE_WAIT_QUEUE_HEAD(gpio_key_wait);

static ssize_t gpio_key_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset){
	int err;
	int key;
	wait_event_interruptible(gpio_key_wait, !is_key_buf_empty());
	key = get_key();
	err = copy_to_user(buf, &key, 4);
	return 4;
}
static struct file_operations gpio_key_drv = {
	.owner	 = THIS_MODULE,
	.read    = gpio_key_drv_read,
};

static irqreturn_t gpio_key_isr(int irq, void *dev_id){
	struct gpio_key *gpio_key = dev_id;
	int val;
	int key;
	val = gpiod_get_value(gpio_key->gpiod);
	
	printk("key %d %d\n", gpio_key->gpio, val);
	key = (gpio_key->gpio << 8) | val;
	put_key(key);
	wake_up_interruptible(&gpio_key_wait);
	return IRQ_HANDLED;
}

/* 1. 从platform_device获得GPIO
 * 2. gpio=>irq
 * 3. request_irq
 */
static int gpio_key_probe(struct platform_device *pdev){
	int err;
	struct device_node *node = pdev->dev.of_node;
	int count;
	int i;
	enum of_gpio_flags flag;

	count = of_gpio_count(node);
	if (!count){
		printk("%s %s line %d, there isn't any gpio available\n", __FILE__, __FUNCTION__, __LINE__);
		return -1;
	}

	gpio_keys_100ask = kzalloc(sizeof(struct gpio_key) * count, GFP_KERNEL);
	for (i = 0; i < count; i++){
		gpio_keys_100ask[i].gpio = of_get_gpio_flags(node, i, &flag);
		if (gpio_keys_100ask[i].gpio < 0){
			printk("%s %s line %d, of_get_gpio_flags fail\n", __FILE__, __FUNCTION__, __LINE__);
			return -1;
		}
		gpio_keys_100ask[i].gpiod = gpio_to_desc(gpio_keys_100ask[i].gpio);
		gpio_keys_100ask[i].flag = flag & OF_GPIO_ACTIVE_LOW;
		gpio_keys_100ask[i].irq  = gpio_to_irq(gpio_keys_100ask[i].gpio);
	}
	for (i = 0; i < count; i++){
		err = request_irq(gpio_keys_100ask[i].irq, gpio_key_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "100ask_gpio_key", 		&gpio_keys_100ask[i]);
	}

	major = register_chrdev(0, "100ask_gpio_key", &gpio_key_drv);  /* /dev/gpio_key */
	gpio_key_class = class_create(THIS_MODULE, "100ask_gpio_key_class");
	if (IS_ERR(gpio_key_class)) {
		printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
		unregister_chrdev(major, "100ask_gpio_key");
		return PTR_ERR(gpio_key_class);
	}
	device_create(gpio_key_class, NULL, MKDEV(major, 0), NULL, "100ask_gpio_key"); /* /dev/100ask_gpio_key */
    return 0;
}
static int gpio_key_remove(struct platform_device *pdev){
	struct device_node *node = pdev->dev.of_node;
	int count;
	int i;
	device_destroy(gpio_key_class, MKDEV(major, 0));
	class_destroy(gpio_key_class);
	unregister_chrdev(major, "100ask_gpio_key");
	count = of_gpio_count(node);
	for (i = 0; i < count; i++){
		free_irq(gpio_keys_100ask[i].irq, &gpio_keys_100ask[i]);
	}
	kfree(gpio_keys_100ask);
    return 0;
}
static const struct of_device_id ask100_keys[] = {
    { .compatible = "100ask,gpio_key" },
    { },
};
static struct platform_driver gpio_keys_driver = {
    .probe      = gpio_key_probe,
    .remove     = gpio_key_remove,
    .driver     = {
        .name   = "100ask_gpio_key",
        .of_match_table = ask100_keys,
    },
};
static int __init gpio_key_init(void){
    int err;
    err = platform_driver_register(&gpio_keys_driver); 
	return err;
}
static void __exit gpio_key_exit(void){
    platform_driver_unregister(&gpio_keys_driver);
}
module_init(gpio_key_init);
module_exit(gpio_key_exit);
MODULE_LICENSE("GPL");

app代码

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
/*
 * ./button_test /dev/100ask_button0
 *
 */
int main(int argc, char **argv){
	int fd;
	int val;

	if (argc != 2) {
		printf("Usage: %s <dev>\n", argv[0]);
		return -1;
	}

	fd = open(argv[1], O_RDWR);
	if (fd == -1){
		printf("can not open file %s\n", argv[1]);
		return -1;
	}
	while (1){
		read(fd, &val, 4);
		printf("get button : 0x%x\n", val);
	}
	close(fd);
	return 0;
}